A solar eclipse happens when the Moon passes between Earth and the Sun and casts its shadow onto Earth. From inside that shadow, the Sun appears partly or completely covered.
The idea is simple, but the result can feel impossible. The Sun is about 400 times wider than the Moon, yet it is also about 400 times farther away from Earth. That size-and-distance coincidence makes the two disks look nearly the same size in our sky. When the alignment is just right, the small nearby Moon can hide the enormous distant Sun.
The shadow has different zones
The Moon does not cast one simple shadow. It creates a few regions, and each one produces a different eclipse experience.
- The umbra is the darkest central shadow. If you stand inside it, you can see a total solar eclipse.
- The penumbra is the lighter outer shadow. If you stand inside it, you see a partial eclipse.
- The antumbra begins beyond the umbra when the Moon appears too small to cover the Sun. If you stand inside it, you see an annular eclipse, sometimes called a ring of fire.
SolarWatch visualizes these shadow regions on an interactive map and globe so the geometry is not just an abstract diagram. You can scrub through time and watch the shadow move across Earth.
Total, partial, and annular eclipses
During a total solar eclipse, the Moon covers the Sun completely for observers inside the path of totality. The sky darkens, the temperature can drop, planets and bright stars may appear, and the Sun's faint corona becomes visible around the black disk of the Moon.
During a partial solar eclipse, only part of the Sun is covered. Partial eclipses are much more widely visible because the penumbra covers a larger area than the umbra. A city outside the path of totality may still see a dramatic partial eclipse.
During an annular solar eclipse, the Moon is too far from Earth in its elliptical orbit to cover the Sun fully. The remaining sunlight forms a bright ring around the Moon. Annular eclipses are beautiful, but they are never safe to view without certified solar filters because the bright solar surface remains visible.
Why totality is so special
Totality is the only part of a solar eclipse when the Sun's bright photosphere is completely hidden. That is why features like the corona, Baily's beads, the diamond ring effect, and the sudden twilight sky are associated with total solar eclipses.
The path of totality is narrow because the Moon's umbra is narrow by the time it reaches Earth. Two people in the same country can have very different experiences: one may see darkness and the corona, while another only a short drive away sees a deep partial eclipse.
A solar eclipse is local
There is no single eclipse time that works for everyone. The moment of first contact, maximum eclipse, totality, and last contact all depend on your exact location. That is why eclipse planning tools focus on local circumstances: what happens at one selected place.
For example, SolarWatch lets you tap a point on the eclipse map and see contact times, obscuration, magnitude, Sun altitude, and totality duration where applicable. Those local details are what turn a global eclipse event into a plan for one city, hilltop, beach, or campsite.
Sources and related guides
- NASA GSFC explains the basic geometry of solar eclipses, including umbra, penumbra, antumbra, and central eclipse paths.
- NASA Earth Observatory shows how the umbra and penumbra appear from space.
- Next in this series: the four types of solar eclipse, the path of totality, why the Moon looks the same size as the Sun, and solar eclipse safety.
See it in SolarWatch
Open the Solar Eclipse Catalog to browse eclipses from 2000 to 2200, choose an event, and explore the map. Use the Moon shadow simulation to see why one location gets totality while another sees only a partial eclipse.